The importance of efficient sewage systems to modern society is well-known. When such a system is not functioning properly, one does not have to be an expert in civil engineering to notice. Much of a typical sewage system relies on a downward, gravity-driven flow to convey wastewater, which includes sewage; however, because the terrain covered by the system is not completely level, the wastewater sometimes needs to be pumped uphill in order to reach a processing point.
Lift stations are used to effect the conveyance of the wastewater from a lower elevation to higher elevation. Lift stations are particularly useful where an attempt to apply a gravity flow conveyance would result in excessive excavation and construction costs. Moreover, at the lift station, water is separated from the solids in the wastewater. Accordingly, lift stations are a vital component of a sewage system, and a large urban area's system may utilize hundreds of lift stations.
Lift stations are typically in-ground cylinders, ranging from six to twenty-four feet in diameter and ten to thirty-five feet in depth. Components of a lift station include one or more inlet lines, through which the wastewater enters the station; an outlet line, through which the wastewater exits the station; one or more submerged pumps to force the flow of the wastewater through the outlet line; and a float that activates the pump, in a manner similar to a toilet. More specifically, the pumps activate when the wastewater in the station reaches a predetermined level, and they pump the wastewater to the outlet, which is often at a higher elevation than the inlets. Switches turn the pumps off when the wastewater has been pumped below a predetermined level, usually a level just above the pumps.
Many lift stations have no interior pipes connected to the inlets, so the entering wastewater simply falls downward into the central portion of the station and splashes into the wastewater already there. Other lift stations may have a pipe inside the station that carries entering wastewater to a point below the water level, so the wastewater is merely directed toward inlets on the pumps.
When it comes to maintenance, lift stations require manual cleaning, which is a considerable investment of both time and money. This is due, in no small part, to the fact that wastewater includes many solids that float on the surface of the water in the lift station. Such solids may include human and animal waste, toilet paper, hair, and grease, among other materials. Because the pumps turn off before the top of the wastewater (and, hence, the floating solids) reaches the pump, not all solids are pumped out of the lift station.
Solids, then, tend to accumulate toward the bottom of the stations, and their removal is difficult due to the considerable depth of the stations. Not only is such an accretion unpleasant in odor and appearance, but the buildup of solid waste in a lift station can lead to the emission of the very poisonous hydrogen sulfide (H2S) gas. Hydrogen sulfide gas often results from the bacterial breakdown of organic matter in the absence of oxygen. Additionally, lift station walls may corrode if not regularly cleaned.